<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* #app{
            color: red;
        }
        .box{
            color: blue;
        } */
        #app .box p{
            color: red;
        }
        #a{
            color: green;
        }
        .b{
            color: yellow;
        }
        p{
            color: pink;
        }
    </style>
</head>
<body>
    <div id="app">
        <div class="box">
            <p id="a" class="b">hello</p>
            <p>word</p>
        </div>
    </div>
</body>
</html>